Apixaban might be exception, but study lacked power to confirm

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Note that this observational study of individuals undergoing catheter ablation for atrial fibrillation or flutter found no difference in the rate of left atrial thrombus regardless of mode of prior anticoagulation.

Atrial fibrillation (afib) patients treated with continuous non-vitamin K oral anticoagulant (NOAC) therapy still need to be evaluated for thrombi before undergoing catheter ablation, according to a study.

The study found no significant difference in thrombus detection rates in NOAC-treated versus warfarin (Coumadin)-treated patients (4.4% versus 2.9%; P=0.45) evaluated by transesophageal echocardiography (TEE) prior to the ablation procedure, Jim Cheung, MD, of Weill Cornell Medical College in New York City, and colleagues reported in JACC: Clinical Electrophysiology.

"Although continuous NOAC therapy would theoretically circumvent the issues of sub-therapeutic anticoagulation associated with warfarin use, the prevalence of LA [left atrial] thrombus ... in patients prior to catheter ablation was not zero," Cheung and colleagues wrote. "We did not identify a significant difference ... between patients on NOAC versus warfarin therapy despite a higher prevalence of co-morbidities among patients on warfarin.

"This suggests that continuous NOAC therapy does not eliminate the need for TEE prior to catheter ablation of AF," they concluded.

"This is a well done study that demonstrates the necessity to perform TEE prior to catheter ablation of atrial fibrillation or flutter, even if there is continuous therapy with the novel oral anticoagulants for the prior 4 weeks or longer," Bhatt told MedPage Today via email.

"These findings provide an important cautionary note -- for the purposes of cost or efficiency, don't abandon the TEE in this setting," advised Bhatt, who was not involved in the study.

Cheung and colleagues retrospectively evaluated 388 patients undergoing their first TEE prior to catheter ablation of afib or atrial flutter. All patients had been on continuous anticoagulation for at least 4 weeks (median 13 weeks) prior to TEE. Median patient age was 65, and 74% were male. Roughly half (53%) were on warfarin and the other half (47%) were on NOACs.

In addition to no significant difference in LA thrombus detection, the investigators found no significant difference in rates of LA thrombus with dense SEC [spontaneous echocardiographic contrast] between the NOAC-treated and warfarin-treated patients (6% versus 6.3%, P=0.89).

However, Cheung and colleagues reported a significantly higher prevalence of LA thrombus with any SEC in the warfarin-treated group (18% versus 9.8%, P=0.021).

For the patients on NOAC therapy, the rates of LA thrombus detection among the 93 patients on dabigatran (Pradaxa) was 5.4%. In the 62 patients on rivaroxaban (Xarelto), that rate was 4.8%. In the 28 patients on apixaban (Eliquis), the rate was 0%. However, these differences were not statistically significant (P=0.48).

The rate of LA thrombus with dense SEC was 6.5% for dabigatran, 8.1% for rivaroxaban, and again 0% for apixaban. Rates of LA thrombus with any SEC was 10.8% for dabigatran, 11.3% for rivaroxaban, and 3.6% for apixaban. These differences were not statistically significant either.

"The low number of patients on apixaban reflects the later introduction of this drug into clinical use compared to the other NOAC agents during our study period. Therefore, our study was underpowered to assess for differences in LA thrombus and dense SEC detection between the individual NOAC agents," Cheung and colleagues said.

"Future clinical studies are needed to explore this comparison, especially given the absence of any LA thrombus or dense SEC detection among patients on apixaban in our study," they said.

Of the 14 patients with LA thrombus, nine had an eventual resolution of the thrombus after modification of their anticoagulant regimen. Six patients with persistent LA thrombus did not undergo the ablation procedure. Of the patients undergoing the procedure, two experienced embolic events within 30 days.

Limitations of the study, in addition to its retrospective design, included an inability to determine the percentage of time warfarin patients were in the therapeutic range prior to TEE, an inability to determine that NOAC patients were 100% compliant, and a lack of follow-up past 30 days, Cheung and colleagues noted.

"Despite continuous therapy, patients on non-vitamin K oral anticoagulants can still have left atrial thrombus detection by transesophageal echocardiography prior to catheter ablation of atrial fibrillation or flutter. Recognition of risk factors for left atrial thrombus such as congestive heart failure and left atrial enlargement would help identify patients who would benefit most from pre-ablation screening for left atrial thrombus," the investigators concluded.

Bhatt disclosed relationships with Elsevier Practice Update Cardiology, Medscape Cardiology, Regado Biosciences, the Boston VA Research Institute, the Society of Cardiovascular Patient Care, the American Heart Association Get With The Guidelines Steering Committee, the Duke Clinical Research Institute, the Harvard Clinical Research Institute, Mayo Clinic, the Population Health Research Institute, the American College of Cardiology, Belvoir Publications, HMP Communications, Slack Publications, WebMD, Clinical Cardiology, the Journal of the American College of Cardiology, Amarin, AstraZeneca, Bristol-Myers Squibb, Eisai, Ethicon, Medtronic, Roche, sanofi aventis, The Medicines Company, FlowCo, PLx Pharma, and Takeda.

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